Both are good for low light shooting.
You may find a little advantage from the 35mm in low light, as you may be able to hand-hold the camera at lower shutter speeds relative to the 50mm.
Low light shooting does apply to outdoors----if there's not much light outside :)
I'd personally base the choice on what I planned on shooting, as opposed to the small advantage in light-gathering ability you may (or may not) experience in real world shooting of both lenses.
Another poster commented on the 50mm being tight indoors. This is certainly an accurate statement. However, the 50 is great for some indoor shots. For instance, I use the 50 for full body shots of my baby daughter--but I could also use the 35 for those shots. I choose the 50, however, for the shallower depth of field it offers to me. NOTE, however, that I personally use a 50mm 1.4 and a 35 f/2. With those lenses, I do, in fact, find a big differences in the narrow depth of field I can achieve (because I can open up the lens to 1.4 with the 50 and only 2.0 with the 35). With the 1.8s (50 and 35), you should find that the 50 affords you the opportunity to blur the background more, because it has a longer focal length and wider max aperture. However, you will be shooting closer to your subject with the 35mm, so that will help make up some of the difference.
Long and short of this: go to the store. Try both for a while...then pick up one.